Re: Subclassing Gnome2::Canvas

["muppet" <scott asofyet org>]

James Muir said:
> I am able to subclass the aliased canvas and instantiate it while
> passing a parameter, but I cannot do the same with the anti-aliased
> canvas :-( . I would have expected to be able to do this with both
> canvases. Is this a bug or, as usual, am I missing something?

You're missing something.  :-)


> Here's a simple example:
...

> my $canvas = can->new_aa(melon=>'x');
> # my $canvas = can->new(melon=>'x');

You have two different things going on here.  Glib::Object::Subclass aliases
yourpackage::new() to Glib::Object::new(), so the second, commented line
actually resolves to

  Glib::Object::new ('can', 'melon', 'x');

On the other hand, nothing special happens with new_aa(), so that is inherited
normally, and evaluates to this:

  Gnome2::Canvas::new_aa ('can', 'melon', 'x');

However, GNome2::Canvas::new_aa() is an xsub which binds to a non-virtual
class-static method, which takes only one parameter -- the ignored class. 
Even if you take off the extra parameters and just call it as 'can->new_aa()',
it will create a 'Gnome2::Canvas', not a 'can', because it is hardcoded to do
so.  In other words, This Is Not How You Do It.

Either:

a) create your own new_aa() method in your custom package and set it up
correctly, or

b) use the 'aa' property to set up your object, like this:

   $canvas = can->new (aa => TRUE, melon => 'x');

Hint: if you choose a), it will be implemented as b).


-- 
muppet <scott at asofyet dot org>